Changes

Take the metro/tramway to La Joliette or Euroméditerranée Gantès and walk down the main street (Boulevard de Dunkerke) for Dunkerkefor a few blocks. There is the highway North-West (A55) that starts there (it's a bridge going up so it's better to stand at the traffic light just before it). A lot of the cars leaving from that point can take you out of Marseille's metropolis and leave you at Fos-sur-Mer, where the road is only one-lane and it's easy to get another lift.

January 2019: Not a lot of people were driving towards Fos at 11am-2pm. With not much traffic, traffic-light hitching from that spot was more difficult, as there were only a few cars at a time and they didn't stop long enough, and there was nowhere for them to pull over. Maybe going early would've worked better.Also if you give up and get a train to Fos-sur-Mer it's not easy to get on the motorway again. (Ivy ended up sneaking through the big IMERYS factory, jumping a big fence, and walking a bit along the motorway to get to a small Total services. Do not recommend). Update on February 2020: No one stopped in the traffic lights just before the A7 ramp to the highway and there's no really other possibilities Metro to directly jump into that highway from the city. Finally, what it worked for me was to go to a petrol Bougainville station inside the city. In my case, I took the tram and went wslk to the last stop (Arenc), from there I walked until a peculiar petrol station called "Briançon service Métro station" ([https://goo.gl/maps/hDWxuyMwYb2L1y7t7 here link to the place in google maps]) and thumbed up from there. Note that area of Marseille Place is not very safe and the petrol station has not really an indoor space, so I wouldn't recommend to go there at night. Sidenote: There's a very bad air pollution still in Fos-sur-Mer. Personally, I'd recommend to leave that place as soon as possible or even try to not stop by there.town